Hi,
Unfortunately, you have not solved the problem - you have only deactivated the mechanism that reports the problem. The issue with the packets sent by your router looping back to the same router persists, and it may cause another problems in future. I caution you against running your setup like this, especially if you use it for learning - because of the packets being fed back to the router, the behavior of your topology may be different.
Just curious: when you run your router attached to the VirtualBox instance for some time (more than one minute) and reports the IPv6 address conflict (i.e. without the workaround you've suggested earlier), what does the show cdp neighbor show? Does this input contain an entry about this very router? If yes, it definitely confirms the packets being reflected back to the router for some obscure reason.
Do you perhaps have an option of running your GNS3 on another machine, or on another operating system? At this point, I am fairly sure that the problem is somewhere in the way GNS3 ties together a VirtualBox instance and an IOS router instance. However, this is not about solving IOS issues anymore (and it never was as it turns out), this is about possible issue in GNS3 or in your particular setup. Unfortunately, there are many variables in play, including the precise settings of GNS3, VirtualBox, your particular operating system and the software running on it.
Best regards,
Peter
